Gameplay scheduler: extend parallel coverage (worker set growth, particle split, render-queue routing, free-running tick DAG, enforced typed access)

[drsnuggles8]

Follow-up issue draft (post-#453: extend gameplay-tick parallelism)

Title: Gameplay scheduler: extend parallel coverage (worker set growth, particle split, render-queue routing, free-running tick DAG, enforced typed access)

Body:
Follow-up to #453, which shipped the declarative SystemScheduler end-state for this
slice: derived order from Reads/Writes/After/Before channel declarations, the
physics kick/fence split with a game-thread shadow band (Dialogue + Quest run
during the Jolt/Box2D world step), worker dispatch for the audited set
(Abilities ∥ Audio) with solved edges as task prerequisites, and the
ENTT_USE_ATOMIC + Scene-constructor pool pre-warm guards.

Remaining expansion opportunities, each with its enabling work:

1. Inventory — two options, needs a deliberate choice:
   (a) physics shadow: simplest, BUT it currently reads post-physics transforms
   for pickup proximity — the shadow would feed it pre-physics transforms (one
   frame stale), an observable change the Reads(kLocalTransforms) edge currently
   forbids; (b) worker dispatch: needs a deferred-publish GameplayEventBus (queue
   drained at a game-thread barrier) + scene-level deferred entity destruction
   (it already self-defers past its own loop; lift to the executor barrier).
   The bus work also unlocks any future bus-publishing system for workers.
2. Particles — split ParticlesCPU (worker-marked) / ParticlesGPU (main thread
   or render-command-queue routed; per-component UseGPU flag decides membership),
   and per-ParticleSystem member RNG seeded from global-seed × entity UUID
   (independently closes the Architecture: deterministic fixed-timestep simulation loop + seeded RNG (unlocks the existing rollback netcode) #452 sub-emitter determinism gap). Note particles
   already fan out internally via nested Tasks::Launch.
3. SnowDeformers / MorphEval — gather CPU-side in the sim step, submit GL
   work (compute dispatch / SSBO / VBO upload) through the stateless render
   command queue; the cloth pipeline's deferred-VBO-upload pattern is the model.
   MorphEval additionally needs per-entity output buffers (instanced MeshSource
   sharing makes in-place vertex writes collide).
4. Navigation / Animation — intra-system ParallelFor (per-agent path queries;
   per-entity pose sampling — UE does the same via hand-rolled parallel anim
   eval tasks). System-level marking is off the table (nav writes transforms;
   anim touches AssetManager lazy loads).
5. Free-running tick DAG (UE Mass dispatch end-state) — dispatch game-thread-
   pinned systems as named-thread tasks so the whole tick becomes one
   prerequisite-driven DAG with the game thread pumping its named queue.
   Blocked on validating the ported named-thread wait support
   (GTaskGraphAlwaysWaitWithNamedThreadSupport is off-by-default/unvalidated).
6. Enforced typed access — scoped per-system accessors validated against the
   channel declarations (Mass-style FMassEntityQuery enforcement), turning the
   audit table from prose into a compile/debug-time contract. Requires routing
   the 18 system bodies through accessor handles; the channel constants shipped
   in Architecture: replace the hard-coded OnUpdateRuntime sequence with a system scheduler (dependency graph + parallelism) #453 are the naming layer it builds on.
7. Physics shadow growth — any new transform/physics-independent system
   should register between PhysicsKick and PhysicsFence by default; also
   consider hoisting the N>=2 hitch catch-up path (currently fully synchronous)
   to interleave char/world phases across kick/fence pairs if profiling shows
   hitch frames matter.

Acceptance per slice: audit note at the schedule builder, seam/shadow-legality
DependsOn tests extended, parallel==sequential determinism test covers the new
member, kill-switch still bisects.

Score

capability: 5
craft: 1
stability: 3
decay: 3
effort: 13
confidence: 0.5
learning: 8
fun: 5
kano: performance
blocked_by: []
blocks: []

_{Rated per issue-scoring · score = confidence × (capability + craft + stability + decay) / effort, derived by the picker.}

[coderabbitai]

🔗 Related PRs

#305 - ci(physics): retry flaky PhysicsLayerFilteringTest + harden JoltJobSy… [merged]
#484 - Feature/deterministic fixed timestep [merged]
#513 - perf(scene): EnTT owning groups for physics-sync, animation, and particle hot loops (#443) [merged]
#561 - fix(networking): correct prediction/reconciliation and state-lifecycle bugs [merged]
#577 - Architecture: declarative SystemScheduler for OnUpdateRuntime — derived order, physics kick/fence shadow, audited worker dispatch (#453) [merged]

---

🧪 Issue enrichment is currently in open beta.

To disable automatic issue enrichment, add the following to your .coderabbit.yaml:

issue_enrichment:
  auto_enrich:
    enabled: false

💬 Have feedback or questions? Drop into our discord!

[drsnuggles8]

Item 2 (Particles) — done in #588 (both halves).

• Determinism half: each ParticleSystem now owns a per-system FastRandomPCG, seeded from runSeed × entity UUID via ParticleSystem::DeriveSeed at OnRuntimeStart (and a fixed preview seed at OnSimulationStart / edit preview). All emission RNG (emitter, emission-shape samplers, parent + child sub-emitters) is routed off the thread-local global stream. This independently closes the Architecture: deterministic fixed-timestep simulation loop + seeded RNG (unlocks the existing rollback netcode) #452 sub-emitter/particle-jitter determinism gap.
• Parallel half: ParticlesCPU (.Parallelizable(), worker-dispatched) split from ParticlesGPU (unmarked barrier, game thread) by a per-entity UseGPU membership check. Full thread-safety audit recorded at the schedule builder (no GL, no EnTT structural changes, no bus publish, per-system RNG, read-only fenced Jolt query, deadlock-free nested tasks); ctor pre-warm extended; parallel==sequential determinism test drives real workers; kill-switch still bisects.

Not closing this umbrella — remaining items 1 (Inventory), 3 (SnowDeformers/MorphEval), 4 (Navigation/Animation), 5 (free-running tick DAG), 6 (enforced typed access) are untouched.